As a cyan color image forming coupler, compound of phenol type or naphtol type have been used conventionally.
However, cyan images formed from phenol type and naphtol type couplers have a serious problem in color reproducibility, i.e., the special absorption of the image has insufficient sharp cut off at the short wave length's end and an unnecessary absorption, or irregular absorption in green area. By them, the compensation of irregular absorption by masking technique must be applied in case of negative film. And in case of paper, there is no means to compensate so that color reproductivity becomes deteriorated.
Besides, dye image formed by phenol type or naphtol type couplers conventionally used have some problems in preservability. For example, a dye image formed from 2acylaminophenol cyan coupler described in U.S. Pat. Nos. 2,367,531 and 2,423,730 is inferior in heat resistivity and a dye image formed from 2,5-diacylaminophenol cyan coupler disclosed in U.S. Pat. Nos. 2,369,929 and 2,772,162 is inferior in light endurability and a dye image formed from 1-hydroxy-2-naphtamido cyan coupler is insufficient in both of heat and light endurability.
Besides, 2,5-diacylaminophenol cyan coupler described in U.S. Pat. No. 4,122,369 and Japanese Patent Publication to Public Inspection (hereinafter refer to Japanese Patent O.P.I. Publication Nos. 155538/1982 or 2,5-diacylaminophenol cyan coupler having a hydroxyl group in ballast part which is described in U.S. Pat. No. 3,880,661 can not attain satisfactory level in endurability against light or heat or in yellow stain so as to preserve its dye image for a long time. For the solving of these problems, in Japanese Patent O.P.I. Publication Nos. 199352/1988, 250649/1988 and 250650/1988, pyrazoloazole type cyan coupler were proposed.
But, in order to satisfy the absorbing wave length of dye to be formed, an electron attractive group and a hydrogen bond forming group are introduced to these coupler. As to these couplers, it is the most serious problem that coupling activity has been decreased remarkably so that color forming is extremely lowered compared with conventional phenol and naphtol type cyan coupler.